Sr. Backend Engineer, API

X.ai; Greater London; On-site; GBP 107,000 - 262,000; Full time

Benefits offered by this job

Equity

Healthcare

Dental coverage

Cash plan

Income protection

Life insurance

Discounts and perks

Job summary

SpaceXSI is seeking a Senior Backend Engineer, API to design and maintain scalable, reliable backend systems written primarily in Rust. You will own services powering Chat API, Imagine API, Voice API, and related Grok tools, while ensuring robust data handling and security across multiple regions.

You will work with databases like PostgreSQL, Clickhouse, and MongoDB, implement gRPC interfaces, and apply LLM inference techniques using TensorRT.

Qualifications

• 5+ years designing, implementing, and maintaining reliable distributed systems.
• Experience with Rust or C++ is required.

Responsibilities

• Build and maintain the unified inference stack for all inference needs.
• Own and evolve platform services powering Chat API, Imagine API, Voice API, Grok Build and Grok Bot.
• Design, build, and maintain Chat API features including batch, collections, files APIs.
• Implement and operate chat moderation and abuse protection across APIs.
• Build and maintain company-wide logging with Zero Data Retention enforcement.
• Manage multi-region inference deployments, data aggregation, replication, and auth system.
• Participate in follow-the-sun on-call coverage (UK-Japan-US) for reliability.

Skills

Rust

C++

Go

Distributed systems

LLMs

Tools

Docker

Kubernetes

PostgreSQL

Clickhouse

MongoDB

gRPC

TensorRT

Job description

SpaceX was founded under the belief that a future where humanity is out exploring the stars is fundamentally more exciting than one where we are not. Today, SpaceX is actively developing the technologies to make this possible, with the ultimate goal of making life multiplanetary and expanding consciousness to the stars.
SpaceXSI is building Super Intelligence to help humanity understand the universe. Our teams are building the full Super Intelligence stack: from our Colossus supercomputers, to Grok models, to our suite of applications, including Grok Bot, Grok Build, Grok Imagine, Grok Voice, and X. We're creating a powerful flywheel where more compute trains better models, better models power more useful products, and what we learn from people using those products shapes what we build next.

SR. BACKEND ENGINEER, API

We are looking for Backend Engineers to help build and operate highly scalable, reliable production infrastructure. Most of our backend infrastructure is written in Rust. Experience with a compiled language such as Rust, C++, or Go is highly beneficial.

RESPONSIBILITIES:

• Build and maintain the unified inference stack as the single surface area for all inference needs across the company
• Own and evolve the platform services that power Chat API, Imagine API, Voice API, Grok Build, and Grok Bot
• Design, build, and maintain Chat API features including batch API, collections API, files API, and related capabilities
• Implement and operate chat moderation and abuse protection systems across the API and grok.com
• Build and maintain the company-wide logging system for all request types, including enforcement of Zero Data Retention (ZDR) policies
• Manage multi-region inference cluster (IC) deployments, data aggregation, data replication, and the distributed authentication system
• Participate in follow-the-sun on-call coverage (UK-Japan-US) to ensure continuous reliability of the inference platform

BASIC QUALIFICATIONS:

• 5+ years of experience in designing, implementing, and maintaining reliable and horizontally scalable distributed systems
• Experience with Rust or C++

PREFERRED SKILLS AND EXPERIENCE:

• Experience in operating databases such as PostgreSQL, Clickhouse, and MongoDB
• Knowledge of service observability and reliability best practicesExperience with LLM inference engines and serving frameworks (e.g., SGLang, TensorRT, vLLM)
• Experience designing or building with agent SDKs and agent orchestration frameworks
• Experience with Docker, Kubernetes, and containerized applications
• Expert knowledge of gRPC (unary, response streaming, bi-directional streaming, REST mapping)

COMPENSATION AND BENEFITS:

£107,000 - £262,000 GBP

Base salary is just one part of our total rewards package at SpaceXSI, which also includes equity, comprehensive healthcare and dental coverage, cash plan, income protection, life insurance, and various other discounts and perks.

SpaceXSI is an equal opportunity employer. For details on data processing, view our Recruitment Privacy Notice.